Tuesday, 24 April 2012

The two-layer neck guitar is progressing further. Now, it's a very nice,
compact and well-sounding instrument. There are still improvements to
be made, but now that it's playable, I hope to play more and modify
less.

The neck is very flat (as Rick Toone's Exoskeleton neck)
without any wood on the back. I might add a piece of wood to make the
neck thicker and more familiar, but for the time being, playing the thin
neck is fun and works surprisingly well. My thumb still creeps up over
the edge of the neck, and that's not the proper way to play it. As long
as you play with the "correct" classical grip with your thumb behind the
fingers, having a thin neck feels fast and precise.

I've mounted
two of my "current transformer" or CT pickups on the guitar. There's
not enough room underneath the strings for a traditional pickup. The CT
pickups work in the same way as Lace's Alumitone pickup: The
part beneath the strings is the primary coil, which is connected to the
secondary coil (the current transformer), which is at the side of the
main aluminium beam. Magnets are small cylindrical neodymium magnets
mounted in hex blind screws. Since there's only one or few primary
windings under the strings, such pickups can be made very flat. This in
turn allows me to keep the whole instrument rather thin, since I don't
need deep pickup cavities.

On my neck pickup, I use a brass coil with only one primary winding
(made from a 20 x 3 mm brass bar) connected to a secondary coil by an
iron core (the green florist's wire). The secondary coil is home made
using a sewing machine bobbin. The bridge pickup has about 15 primary
windings running through an AS-104 current transformer. They supplement
each other well, the bridge pickup being quite snappy and sharp, while
the neck pickup is more deep and soft.

Both pickups have low
impedance; in the range of microphones, which is why I am using an 500
ohm -> 50.000 ohm line transformer before plugging the guitar into my
amp.

Also added is a string retainer at the headstock end,
keeping the strings from rattling. A bracket for jack, volume pot and
two mini jacks for the pickups makes it easy to plug it into an amp and
to switch the pickups. For intonation, I've added a couple of screws to
the saddles going into the end piece that holds the tuners. By turning
the screws, the saddles are moved back and forth.

I still haven't
added piezo pickups, partly because I haven't figured out where to put
the pre-amp and controls, partly because the CT pickups function so
well.

Next step might be a thicker (6 mm rather than 4 mm)
plastic body, this time bent with a little more care. The one I'm using
now has been bent into shape using a heat gun and brute force. Another
improvement could be a piece of wood on the plastic body that acts as
forearm support - the curve of the body makes it hug the torso of the
player (which is nice and gives good control of the guitar), but there's
nothing on which to rest my arm, and that becomes a bit tiresome.

There's only one aspect that I'm not quite satisfied with: The bow of the neck is not easily adjustable. This is due to the strength of the beams - even without tightening one against the other, the pair of them are enough to counteract the pull of the strings, so there really isn't much to adjust. A solution could be a thinner back beam, but I am not sure they are available in the necessary width.

Thursday, 12 April 2012

Improvements since last post:
Saddles modified -> lower action
Transparent plastic body (styrene-acrylonitrile) added.
Two screws at the bottom side of the head end holding the two layers of the neck together.
Row of neodymium magnets in M4 blind screws for current transformer pickups.

Future improvements:
String guide - pressing down on the strings before the zero fret, since they tend to rattle.
Row of magnets for current transformer pickup in bridge position.
Screw holes making the saddles lengthwise adjustable for intonation.
Piezo pickups and amplifier.
Jacks, switches, pots etc. I plan to put the electronics on the plastic body rather than on the beam itself.